Lamp having two separate phosphor coatings

ABSTRACT

A lamp comprises an envelope within which is disposed a source of electromagnetic radiation. A coating of a &#39;&#39;&#39;&#39;high-temperature phosphor&#39;&#39;&#39;&#39; and coating of a &#39;&#39;&#39;&#39;low-temperature phosphor&#39;&#39;&#39;&#39; are provided on discrete regions of the inner surface of the envelope of the lamp so as to operate at respectively a higher and lower temperature during normal working of the lamp.

uuucu mates ratent 11113, 34,715

72] Inventors Eric John George Beeson; 56] Refe n e Cited Horace EdwardStanyon, both of London, UNITED STATES PATENTS 21 A l N 33 's? 2,748,3035/l956 Thorington 313/25 1 l 1 P 2,785,327 3 1957 Anderson 313/25 [22]Filed Apr. 13, 1970 3,025,423 3/1962 Rimbach 313/108 [45] Patented 19723 480 819 11/1969 Faria et al 313/109 [73] Assignee Thorn LightingLimited London, Enghmd FOREIGN PATENTS [32] Priority Apr. 15,19691,273,385 7/l968 Germany 3l3/l09 [33] Great Bram Primary Examiner- RoyLake [31] l9304/69 Assistant Examiner- Palmer C. Demeo At!0rneyOwen J.Meegan [54] LAMP HAVING TWO SEPARATE PHOSPHOR COATINGS ABSTRACT: A lampcomprises an envelope within which is 4 Claims 5 Drawing disposed asource of electromagnetic radiation. A coating ofa [52] US. Cl 313/109,high-temperature phosphor" and coating ofa low-tempera- 313/25, 313/112,350/317 ture phosphor" are provided on discrete regions of the inner[51] Int. Cl H0lj 61/48 surface of the envelope of the lamp so as tooperate at respec- [50] Field of Search 3 13/109, tively a higher andlower temperature during normal working 25,112, l84,ll3;350/317 3llofthe lamp.

[6 5C 350C 380C PATENIEBMI 1 I972 3.634715 SHEET 1 BF 3 ERIC JOHN GEORGEBEESON HORACE EDWARD STANYON INVENTORS BYC/W f w ATT RNEY PATENTED m: 11972 3634171 5 SHEET 2 [IF 3 4 TEMR 55C 'TEMR' 245C TEMP 400C \1 a: u. 550 rv/womzrms ERIC JOHN GEORGE BEESON HORACE EDWARD STANYON INVENTORS ATORNEY 1 ENERGY ENERGY SHEET 3 [1F 3 H04. TMR400C TEMP 240C TEMR 60CNANOMETERS NANOMETERS ERIC JOHN GEORGE season HORACE EDWARD smmow NTORSBY TORN LAMP HAVING TWO. SEPARATE IIIOSPHOR COATINGS The presentinvention relates to lamps which phosphors are irradiated byelectromagnetic radiation so as to emit visible light.

During the operation of such a lamp, heat energy is transferred to thephosphor causing its temperature to rise. Fora given phosphor,undergoing a particular excitation, there will be a relationship betweenthe temperature of the phosphor and the amount of light emitted. In somecases the phosphor emits more light as the temperature is raised: inothers the amount of light emitted falls with increasing temperature.

The total light output of such a lamp is made up by the light emitted bythe phosphor plus the part of the irradiating radiation that is withinthe visible region of the spectrum.

The source of the irradiation in such a lamp may conveniently be amercury arc-tube.

, The color rendition properties of such a lamp suffer because of thelack of certain wavelengths in light emitted by the discharge tube,there being present only light of the bands of wavelengthscharacteristic of the discharge. In an attempt to improve the colorrendition properties phosphors are included in the lamp, the lightemitted from which is of such wavelengths as will complement the visiblelight output of the discharge tube by providing some of the missingwavelengths.

According to the present invention there is provided a lamp comprising asource of electromagnetic radiation mounted within an envelope of thelamp, a coating of a high temperature phosphor provided on a firstregion of the inner surface of the envelope provided on a second regionof the inner surface of the envelope, the first region of the envelopehaving a higher working temperature during normal operation of the lampthan the second region.

In this specification the expressions high temperature phosphor" and lowtemperature phosphor mean respectively a phosphor having a maximumoutput of light for the excitation occurring in normal working of thelamp at a higher temperature and a phosphor having a maximum output oflight for the excitation occurring in normal working of the lamp at alower temperature.

The lamp may include more than two phosphors, the, or each, furtherphosphor being so arranged as to operate at a predetermined temperaturedependent on the relationship between its emission of light andoperating temperature.

The invention will now be described by way of example with reference tothe accompanying drawings, in which:

FIG. 1 shows a reflector type lamp operating in a vertical condition;

FIG. 2 shows an elliptical lamp operating in a horizontal condition;

FIG. 3 is a graph showing the variation in the temperature of the amountof light emitted by phosphor 13;

FIG. 4 is a graph showing the variation with temperature of the amountof light emitted by phosphor A, and

FIG. 5 shows the total light energy output of the lamp shown in FIG. 1.

FIG. 1 shows diagrammatically a reflector bulb type lamp. This bulb isarranged to operate with its axis vertical and its capped end uppermost.The temperature distribution on the outer envelope of the bulb isindicated in FIG. 1. The envelope carries on its inner surface twodiscrete phosphor coatings. A coating of a first phosphor, phosphor A,is arranged on a portion of the envelope having a relatively highoperating temperature and a coating of a second phosphor, phosphor B, isarranged on a portion of the envelope having a relatively low operatingtemperature.

The variation of the amount of energy emitted by phosphor A 'at various.temperatures is shown in FIG. 4 and that for phosphor B in FIG. 3. Itis clear that for the lamp to operate at maximum light outputefficiency, the operating temperature of phosphor A should be between240 and 400 C. and that of phosphor B between 55 and 245 C. This isensured by limiting the coating of phosphor A to the region nearer thecap which, in normal operatin conditions, will be at a highertemperature than the region urther from the cap on which the coating ofphosphor B is provided.

The particular phosphors used in the lamp are chosen by reference toknown light emission/temperature characteristics of phosphors. In theexample described above phosphor A is yttrium-vanadate and phosphor B ismagnesium fluorogermanate.

FIG. 5 shows the total output of the lamp in the visible region of thespectrum. The square peaks are the output of the mercury arc-tube in thevisible region and the smoother peaks the contributions from phosphors Aand B. It is seen that the light from the phosphors fills in bands ofthe spectrum in which the mercury arc-tube is deficient.

Although in the embodiment described above only two phosphors are shown,it is possible to use more than two phosphors. In a further embodiment,a coating of a third phosphor is provided at a position in which itsoperating temperature will be intermediate that of phosphor A andphosphor B such a phosphor could be europium activated strontiumsilicate coatings a more complete visible spectrum can be built up toprovide an increase in total lumens and to improve the color renditionproperties of the lamp.

In an alternative embodiment FIG. 2 is shown. This embodiment shows anelliptical lamp which is adapted for mounting in a fitting to operate ina horizontal condition. During such operation, there is a temperaturedifferential between the top and the bottom of the lamp. Phosphor A iscoated on the upper part of the inner bulb surface and phosphor B on thelower part. The approximate temperatures shown in FIG. 2 are for thelamp operating in free air. The temperature would be higher if the lampwere operated within a fitting in which case the fitting design willinfluence the final temperature differential.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A lamp comprising:

an envelope,

a source of electromagnetic radiation within said envelope,

a first region on the inner surface of the envelope being adapted to runat a relatively high temperature,

a second region on the inner surface of the envelope being adapted torun at a relatively low temperature,

a coating of a high temperature phosphor" disposed on said first region,

a coating of a low temperature phosphor disposed on said second region.

2. A lamp as claimed in claim 1, wherein one end of the envelope isclosed by a cap and the lamp has a normal working position in which itsaxis is vertical and its capped end uppermost, said first region beingnearer said capped end than said second region.

3. A lamp as claimed in claim 1 in which the high temperature phosphoris yttrium-vanadate.

4. A lamp as claimed in claim 1, wherein the low temperature phosphor ismagnesium fluorogermanate.

2. A lamp as claimed in claim 1, wherein one end of the envelope is closed by a cap and the lamp has a normal working position in which its axis is vertical and its capped end uppermost, said first region being nearer said capped end than said second region.
 3. A lamp as claimed in claim 1 in which the ''''high temperature Phosphor'''' is yttrium-vanadate.
 4. A lamp as claimed in claim 1, wherein the ''''low temperature phosphor'''' is magnesium fluorogermanate. 